Question

An `N×N` table is filled with numbers such that all rows are distinct (differing in at least one position). Prove that it is possible to delete a column such that in the remaining table all rows are also distinct.
(a) Hint

Difficulty level (1 very easy - 10 very hard): 8

Combinatorics -> Pigeonhole Principle Combinatorics -> Graph Theory Proof and Example -> Proof by Contradiction

Sources:

Tournament of Towns, 1979-1980, Main, Spring Question 2

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